With the constant development of deepsea diving technology, divers have worked at increasingly greater depths and now routinely descend to depths as much as 1000 feet below sea level. The diving techniques are based upon the principle of maintaining the divers under pressure for a long period of time, so that they undergo lengthy decompression only at the end of a tour of duty. The principal habitat of the diver during his operational tour is a surface hyperbaric chamber maintained at approximately the pressure that is to be encountered at working depth. When the diver must descend, he is transferred directly into a pressurized diving bell and lowered by a cable system to the work location. At this depth pressures are substantially equalized so that the diver can leave the bell to perform his assigned inspection or maintenance duties. The diver then returns to the bell, which is held pressurized for the return to the surface and the habitat.
In accordance with modern practice, the high pressure breathing gas in the hyperbaric chamber and the bell is predominantly helium and a small percentage of oxygen which provides an oxygen intake equivalent to that at sea level. The high helium content, however, creates a highly heat conductive environment about the diver, from which thermal energy is constantly lost to the cold (typically 0.degree. C. to 5.degree. C.) seawater. Thus the breathing mixture must constantly be heated, or the diver must be in a heated suit, or both. The losses are such that the temperature must be closely regulated or the diver suffers extreme discomfort. For safety and reliability the energy sources for the diving bell are supplied and regulated from the surface.
Diving at such extreme depths is of course hazardous work, not only because of the extreme conditions encountered but also because of the mechanical problems involved in lowering and raising a diving bell over long distances at the end of a cable. The diving bell must be designed to accommodate one or two divers, and must have an adequately pressure-resistant shell without being so large and cumbersome that it cannot be transported without prohibitively costly and massive equipment. Consequently, diving bells typically have little more interior space available than that needed to accommodate the divers. Thus only limited provisions can be made for survival of the divers in the event of catastrophic failure or impairment of a part of the diving system. If a cable breaks, for example, the heating and breathing gas mixture flows from the surface are terminated, and the diving bell descends to the ocean floor. The diving bell incorporates provisions for sealing in the divers under these circumstances, but emergency measures must be undertaken to maintain adequate life support for the divers for a given maximum time, usually 24 hours. This is deemed a sufficient interval for reconnecting a cable to or freeing the bell so that it can be drawn to the surface. In this conjunction, the high pressure, highly heat conductive atmosphere within the diving bell poses extreme hazards even though it provides sufficient breathing gas. The diving bell is large enough to contain spare high pressure breathing gas tanks but cannot contain units or devices that could generate sufficient thermal energy to supply the lost heat. Consequently the temperature in the diving bell rapidly begins to lower to the temperature of the surrounding ocean depths. The pressurized helium conducts heat away from the diver's body so rapidly that it functions as the equivalent of a wind chill factor in the range of -100.degree. C. At such depths, survival is not even conjectural unless some means are provided for maintaining a reasonable body temperature for the diver. Conventional devices and systems that can be used under normal circumstances are wholly inadequate for this purpose. In addition, chemicals that are used to scrub the breathing gas mixture of carbon dioxide do not work well when cold or dry, so that the diver is further endangered in the emergency situation.